Dean and John would probably be pretty careful not to slip up in front of Sam. Nothing if he’s in the room, even if he’s dead asleep; same goes for the car (although Dean pushes it on occasion when he grabs his dad’s dick in the front seat, and always feels him harden a little before he shoves Dean away again). If Sam’s with them and they really can’t wait then only in the shower after he’s asleep.
But that doesn’t mean Sam doesn’t come home from school and find Dean flushed and disheveled and kind of dazed, or that he doesn’t see the marks on his neck, back, legs when they change in the same room. And he definitely doesn’t miss the longing in Dean’s eyes while he watches Dad’s fingers disassembling and reassembling weapons, or the way Dad sometimes looks at Dean like he’s starving, or the random heaviness in the room when Dad won’t look at either of them, his shame almost palpable. It’s hard not to notice.
And so at some point Sam starts lying about when he’s gonna be home and then coming back early, and he isn’t surprised when he hears the noises, John grunting and Dean moaning and whining and gagging. And when he starts getting hard listening to it he ignores it, because like, obviously it’s not about THEM, it’s just that he’s a horny teenager and it’s sex, and any kind of sex is always gonna have that effect on him, right? It’s not like he wants to join in. He hates Dad, he hates the thought of Dad’s hands all over Dean, especially since Dad doesn’t even really KNOW Dean like Sam does, doesn’t really care about him enough to.
That’s the only reason he listens, as often as he can, because he cares about his brother. He’s looking out for him, just like Dean always looks out for Sam. He’s not going to let Dean get hurt. He would never let him get hurt, not ever.
It should be him with Dean, really. He would make sure Dean liked it, he would make him come over and over again. He would treat him right. Wait, what?
